The invention relates to toothbrushes, and more particularly relates to powered toothbrushes. In its most immediate sense, the invention relates to a brush tip for a powered toothbrush having two counter-rotating heads that rotate on a common axis.
In a conventional motorized toothbrush of the multi-head type, a disposable brush tip is detachably secured to the handle of the toothbrush. The tip has a plurality of brush heads, which oscillate (as by rotation) under the power of the motor. Each brush head has a plurality of tufts of bristles.
Existing motorized toothbrushes have relatively small xe2x80x9ccoveragexe2x80x9d, i.e. they do not clean large surface areas at one time. This is because the brush heads are relatively small. If they are made too large, they will put an excessive load on the motor.
Furthermore, some users operate such toothbrushes improperly. Instead of applying only light pressure, they force the bristles hard against the teeth. Under such conditions, the distal end of each tuft of bristles stays in the same place and the tufts twist themselves tightly in alternate directions. This makes the brushing less effective, because the bristles do not scrub the surfaces of the teeth.
It would be advantageous to provide a multi-head motorized toothbrush that would have greater coverage than conventional toothbrushes.
It would also be advantageous to provide a multi-head motorized toothbrush that would perform better even when the user applies excessive pressure against the tooth surfaces to be cleaned.
In accordance with the invention, a brush tip for a motorized toothbrush has a first brush head and a second brush head. The second brush head encircles the first brush head, and means are provided for differently accelerating the first and second brush heads in response to motion produced by the toothbrush motor.
Because the second brush head encircles the first brush head, the two head together have a relatively large area and, therefore, greater coverage. And, because the two brush heads are accelerated differently, their bristles do not twist themselves together even when pressed hard against the teeth.
In preferred embodiments, the first and second brush heads are accelerated in opposite directions, the first brush head is circular, and the second brush head is elliptical. The elliptical brush head provides greater coverage than a circular brush head and the opposite motions of the heads make it impossible for the bristles attached to the first brush head to twist into the bristles attached to the second brush head.
For toothbrushes of the type wherein the motor produces oscillating rotational motion of a shaft, a gear is mounted at the end of the shaft and is used to rotate the brush heads. For toothbrushes of the type wherein the motor produces reciprocating linear motion of an actuator, two connecting rods are used to convert this linear motion into oscillating rotational motion of the brush heads.
Such a brush tip is disclosed in commonly-owned pending patent application Ser. No. 09/338,750, filed Jun. 23, 1999, issued on Feb. 26, 2002 as U.S. Pat. No. 6,349,442, the entire disclosure of which (including the drawings) is hereby incorporated herein by reference. That pending patent application discloses two different head rotation mechanisms, each designed for use with a particular type of motorized toothbrush. One mechanism is designed for use with a motorized toothbrush wherein an actuator, such as a plunger, is linearly reciprocated. The other mechanism is designed for use with a motorized toothbrush wherein a shaft is rotationally oscillated.
Motorized toothbrushes generally use a battery-powered DC motor as a source of mechanical energy. This mechanical energy takes the form of a one-way rotation of a shaft that is mechanically coupled to the rotor of the DC motor. Therefore, for the above-discussed mechanisms to be usable, the motorized toothbrush must include a motion conversion mechanism that converts the one-way shaft rotation produced by the DC motor into linear reciprocation or into rotational oscillation. This increases cost of manufacture, diminishes power available to the toothbrush heads, and increases noise of the toothbrush during use. It would be advantageous to provide a brush tip for a motorized toothbrush wherein one-way rotation of a shaft can be used as the mechanical input to drive two counter-rotating heads that rotate about a common axis.
Furthermore, the mechanisms disclosed in the above-referenced allowed patent application require adjustment during assembly. Such adjustment has associated costs. It would be advantageous to provide a brush tip of this type that could be assembled with less adjustment, and therefore at reduced cost.
In accordance with the invention, first and second brush heads are provided. The first brush head is mounted for rotation about a brush head axis and has a first slot extending generally normal to the brush head axis. The second brush head encircles the first brush head, and is mounted for rotation about the brush head axis. The second brush head has a second slot extending generally normal to the brush head, and the first and second slots are on the same side of the brush head axis. And, an elongated shaft is provided. The shaft is mounted for rotation about a shaft axis, has a proximal end and a distal end, and forms first and second cranks. The first crank is located at the distal end of the shaft and engages the first slot, the second crank is located intermediate the first crank and the proximal end of the shaft and engages the second slot, and the cranks are offset with respect to each other.
This brush tip is suited for direct connection to a DC motor in the motorized toothbrush; the shaft can be coupled to the shaft of the motor without the need for an intermediate mechanism to change the rotation of the motor to linear reciprocation or rotational oscillation. And, assembly requires little adjustment because it is only necessary to drop the brush heads over the shaft so that the first slot and second slot engage the first and second cranks respectively. Alternatively, the brush tip can be assembled by simply pushing the distal end of the shaft through the second slot of the second brush head and into the first slot of the first brush head; in this instance, both the brush heads rotate until the second crank engages the second slot.
Advantageously, the shaft is a serpentine metal element, the first and second cranks extend away from the shaft axis in opposite directions, and the cranks occupy a common plane that contains the shaft axis. Such a shaft can be easily and inexpensively manufactured (as by stamping or bending).
In a particularly advantageous embodiment, the second brush head has an interior recess adjacent the second slot and a washer is mounted on the shaft between the first and second cranks so that it is located in the recess. As the shaft rotates, the washer keeps the first and second brush heads spaced apart, thereby preventing them from xe2x80x9cchattering,xe2x80x9d i.e. from striking against each other as they rotate). This reduces noise during operation.
In accordance with the invention, the first brush head has a first set of bristles secured thereon forming a circular pattern and the second brush head has a second set of bristles secured thereon forming an elliptical pattern. The elliptical pattern on the second brush head provides a greater coverage than a conventional circular pattern and the opposite rotating motions of the first and second brush heads prevent the bristles from the first and second brush heads from twisting into each other.